“Never say diet”

“Never say die” is a phrase cited in print from at least 1814.
 
“Never say diet” has been the title of several weight-reducing books and articles, including a 1980 book by exercise guru Richard Simmons. “Never say diet” has been cited in print since 1906.
 
 
The Yale Book of Quotations
Edited by Fred R. Shapiro
New Haven, CT: Yale University Press
2006
Pg. 617 (Proverbs):
Never say die.
Diary of Benjamin F. Palmer, Privateersman (1814).
 
Narrative of a Journey in the Interior of China,
And of a voyage to and from that country in the year 1816 and 1817
By Clarke Abel
London: Longman, Hurst, Rees, Orme, and Brown
1818
Pg. 258:
“Never say die my lads,” was a certain appeal to the energy and the pride of his men.
   
Google Books
Naval Sketch-Book
By William Nugent Glascock
Vol. II
London: Cox and Baylis
1826
Pg. 32:
“Tip us your dadule,” says I—never say die—and send like a mugen, and book us a breth in the mail.”
 
Google Books
The Altogether New Cynic’s Calendar of Revised Wisdom for 1907
By Ethel Watts-Mumford Grant, Oliver Herford and Addison Mizner
San Francisco, CA: Paul Elder and Company
1906
(Not paginated—ed.)
Never say diet!
   
17 November 1906, Trenton (NJ) Evening Times, pg. 8, col. 1:
THE ALTOGETHER NEW CYNIC’S CALENDAR OF REVISED WISDOM FOR 1907. By Ethel Watts-Mumford Grant, Oliver Herford and Addison C. Mizner. Paul Elder and Company, New York. 75 cents.
(...)
“The First Cynic” and “The First Quarrel” are quote as clever as “The First Monday” of the last year’s volume, the success that was pirated and plagiarized to an unlimited extent; and “Never say diet” and “Many looks spoil the cloth” have a pointed shaft for the foibles of today.
 
13 April 1922, Trenton (NJ) Evening Times, pg. 1:
Being thin, our slogan is: “Never say diet.”
 
OCLC WorldCat record
Never say diet; how to live older and look longer.
by Corey Ford
Type:  Book; English
Publisher: New York, Holt [1954]
   
8 July 1971, Dallas (TX) Morning News, section E, pg. 10:
Never Say Diet, Just Do It
By FREDRICK J. STARE
Department of Nutrition
Harvard University
 
OCLC WorldCat record
Richard Simmons’ Never-say-diet book.
by Richard Simmons
Type:  Book; English
Publisher: New York : Warner Books, ©1980.
 
OCLC WorldCat record
Never say diet!
by Nicole Parton; Judy Toews
Type:  Book; English
Publisher: Toronto : Key Porter, 1998.
   
OCLC WorldCat record
Never say diet : make five decisions and break the fat habit for good
by Chantel Hobbs; Rowan Jacobsen
Type:  Book; English
Publisher: Colorado Springs, Colo. : Waterbrook Press, 2007.